1. Technical Field
The present invention relates to technology for enabling a cable modem (CM) to transmit an upstream signal synchronized with a cable network over an optical Internet Protocol (IP) network using signals transmitted and received between the CM and a Cable Modem Termination System (CMTS).
2. Description of the Related Art
A cable broadcast network provides services, such as a digital broadcast service, the Internet service, and the like, using a Hybrid Fiber and Coaxial (HFC) network. The HFC network is configured with a combination of optical fiber and coaxial cable. In the case of a conventional HFC network, a coaxial cable line is about 1 km long. However, recently, in order to accommodate interactive and smart services, the architecture is developed such that optical fiber is extended so as to be closer to subscribers (Deep Fiber) or so as to reach all the way to subscribers (Fiber To The Home (FTTH)).
Multi-System Operators (MSOs) continuously attempt to introduce fiber-optic services in new service areas. In order to provide a cable broadcast service based on an optical network, RF/PON, through which a broadcast is transmitted in the form of Radio Frequency-Overlay (RF-Overlay) and in which two-way signaling and data services for the broadcast are provided using Internet-Protocol (IP) packets over a Passive Optical Network (PON), has been attempted. However, RF/PON faces obstacles to commercialization because it is expensive to replace existing cable infrastructure, such as Set-Top Boxes (STBs) and the like. As an alternative, RF over Glass (RFoG), through which a downstream signal is delivered in the form of RF-Overlay to an STP via optical fiber and an upstream RF signal from the STP is delivered through optical transmission, has also been attempted, but RFoG is not widely used due to implementation costs, such as that of an electro-photic conversion device and the like.
As a solution to the cost-related problems, such as electro-photic conversion device costs and costs for replacing existing infrastructure, a method in which an analog RF signal transmitted from a subscriber's terminal, such as an STB or the like, is digitized and is transmitted over an optical IP network, such as Ethernet PON (EPON), Gigabit PON (GPON), or the like, and in which the upstream signal, transmitted from the STB over the IP network, is converted into an analog RF signal at the headend and is then transmitted to a Cable Modem Termination System (CMTS), has been proposed. However, when an upstream signal is transmitted as described above, because multiple Cable Modems (CMs) on the subscriber's side share a single physical medium, the CMs must transmit their data according to a synchronous time-division multiplexing method, that is, the CMs must transmit data during time slots allocated thereto by the CMTS. Therefore, the present invention intends to provide a method for synchronizing upstream data based on the Data Over Cable Service Interface Specification (DOCSIS) with an existing cable broadcast network and transmitting the same over an optical IP network.
The above-described information about the related art has been retained by the inventors for the purpose of developing the present invention or was obtained during the process of developing the present invention. Also, it should be appreciated that this information did not necessarily belong to the public domain before the patent filing date of the present invention.